Excellent energy storage density and charge–discharge performance of a novel Bi0.2Sr0.7TiO3–BiFeO3 thin film
Lead-free (1−x)Bi0.2Sr0.7TiO3–xBiFeO3 (x = 0–0.4, denoted as BST–xBFO) thin films were deposited on Pt(111)/Ti/SiO2/Si substrates by a sol–gel/spin coating technique and their microstructures, dielectric properties and energy storage were investigated in detail. A single perovskite phase and high-density microstructure are obtained in all thin films. Moreover, the hysteresis loss in the BST–xBFO system is relatively low accompanied by high breakdown strength. An excellent energy storage density of 48.5 J cm−3 with an efficiency of 47.57% is obtained under high breakdown strength ∼4800 kV cm−1 in a 0.9BST–0.1BFO thin film capacitor. This capacitor also presents excellent thermal stability with minimal variation of both the energy storage density (<13%) and efficiency (<15%) in a wide temperature range (30–120 °C). What's more, the 0.9BST–0.1BFO thin film capacitor possesses a fast discharge speed with a release time of 0.22 μs. All results strongly suggest that the lead-free 0.9BST–0.1BFO thin film is a promising material for energy storage applications. More importantly, BST–xBFO is a recently developed new system and the findings could provide new ideas about the design and fabrication of lead-free dielectrics with high energy storage density and fast charge–discharge speed.